Power quality is an all-encompassing concept for a multitude of individual types of power system disturbances. The presence of harmonics in power supply network poses a severe power quality problem that results in greater power losses in the distribution system, interference problems in communication systems and, sometimes, in operation failures of electronic equipment. Shunt active power filters are employed to suppress the current harmonics and reduce the total harmonic distortion (THD).
The voltage source inverter (VSI) is the core of an active power filter. The hysteresis current control is a method of controlling the VSI. Hysteresis control can be either of fixed band type or adaptive band type. In this paper, Synchronous Reference Frame (SRF) theory is implemented for the generation of reference current signals for the controller. This paper investigates the effectiveness of the proposed model in harmonics currents mitigation by simulating a model of a three-phase three wire shunt active power filter based on adaptive hysteresis current control and SRF theory. Simulation results indicate that the proposed active power filter can restrain harmonics of electrical source current effectively
- Synchronous reference frame theory
- Adaptive hysteresis control
- Harmonic mitigation
- Shunt active filter
- Voltage source inverter
Fig. 1. Reference Current Generation Block
EXPECTED SIMULATION RESULTS:
Fig. 2. Nonlinear Load Currents
Fig. 3. Compensating APF Currents
Fig.4.Source currents after compensation
Fig.5. Harmonic analysis of source current with Adaptive Hysteresis Band
In the adaptive band hysteresis control, the switching frequency is nearly constant with respect to the system parameters and defined switching frequency. However, at low switching frequency case, the tracking is not as good as the one in high switching frequency. Obviously, a decrease in switching frequency results in an increase in the hysteresis bandwidth that causes the free operation of current error in a wider range.
This higher low-frequency error, in turn, will lead to higher low order harmonics in the source current, and hence higher THD. Based on the above facts, the switching frequency should be kept as high as possible for better performances of adaptive band hysteresis current control.
The developed model has the following advantages:
- Simplification of the power conversion circuit can be achieved.
- (ii) Under the developed model, the performance of control strategy can be effectively examined without long simulation run time and convergence problem.
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